Human hepatocellular carcinoma (HCC) is one of the most serious complications of chronic liver disease and cirrhosis. Even more disturbing is the observation that the average life expectancy from the time of diagnosis is approximately eight to ten months. The incidence of HCC has begun to increase in the United States principally due to the contribution of chronic hepatitis C (HCV) infection. In addition, with the obesity epidemic including Type II diabetes and insulin resistance, the emergence of non-alcoholic steatohepatitis (NASH) has begun to assume a larger role in the pathogenesis of this devastating disease due to the development of cirrhosis, a risk factor for HCC. More recently, there is widespread concern among health care professionals regarding the increase in HCC and the lack of optimal screening techniques that lead to or contribute to early diagnosis and treatment in the hope of improving the prognosis of this almost uniformly fatal disease. Thus, the purpose of this proposal is to validate a new marker that may be useful in the early diagnosis of HCC. In this regard, we have identified by monoclonal antibody (mAb) binding and expression cloning, a cell surface protein marker that is enhanced in HCC tumors. The gene encoding for this protein has been cloned and molecularly identified as aspartyl (asparaginyl) ([unreadable]-hydroxylase (HAAH) which appears to be highly expressed in most (>90%) hepatitis B (HBV) and HCV related HCC. Furthermore, this protein appears to be present in serum of such patients. Thus, we have established immunoassays to detect C and N terminal fragments as well as full length HAAH in serum using recombinant proteins as standards. Because this enzyme is expressed on the cell surface, we have recently developed human scFv and IgG antibodies directed against the various region of the molecule. These reagents will be used in biodistribution studies to target tumors in murine models of human HCC. Evidence will be presented to support the hypothesis that HAAH gene is a novel biomarker for HCC since expression appears to be highly associated with the pathogenesis of the disease. We plan to do the following. Specific Aim 1. Validate HAAH as a biomarker for HCC. Specific Aim 2. Further characterize human scFv fragments and IgG anti-AAH antibodies. It is likely that these new mAb based assays will be useful for the early detection of HCC and human anti-HAAH antibodies may be employed as targeting reagents for the specific detection of HCC in the liver.